Titanium base alloy



United States Patent 3,343,951 TITANIUM BASE ALLOY Roger E. Peebles, Steubenville, Ohio, assignor to Titanium Metals Corporation of America, New York, N.Y., a corporation of Delaware No Drawing. Filed Mar. 1, 1965, Ser. No. 436,268 4 Claims. (Cl. 75175.5)

at the same time be ductile and weldable so that it may be shaped, formed or fabricated as desired. The properties imparted by conventional alloying elements are to a degree known but the effects of additions of such individual elements, while improving some characteristic or characteristics, often have a deleterious effect on some other property. For example, the strength of titanium at elevated temperature can be markedly increased by addition of aluminum as an alloying element, but, beyond a given maximum, at a sacrifice in ductility and generally thermal stability.

A need, therefore, exists for an alpha-type titanium base alloy having the combination of lightness, elevated temperature strength, stability and creep resistance, as well as toughness, weldability and ductility, and having all these properties at a level equivalent or superior to heretofore known alloys having less than all and characterized by a serious deficiency in one or more of them.

Summarized briefly, this invention provides such an alloy having such combination of properties, and this alloy consists essentially of by weight from 5.5% to 6.5% aluminum, from 1.7% to 2.3% tin, from 0.7% to 5% zirconium, from 0.7% to 3.0% molybdenum, and up to 0.2 oxygen, balance substantially titanium and incidental impurities. A preferred alloy consists essentially of about 6% aluminum, about 2% tin, about 2% zirconium and about 1% molybdenum, up to 0.12% oxygen, balance substantially titanium. Another preferred alloy consists essentially of about 6% aluminum, about 2% tin, about 4% zirconium, about 2% molybdenum, up to 0.12% oxygen, balance substantially titanium. The latter alloy is slightly stronger than the former, and is most useful where it strength is valuable in spite of its slightly increased density. The alloying elements present 'within the defined ranges are necessary to provide the combination effect resulting in the mechanical properties of the alloy of this invention. The percentages of alloy constituents referred to herein are in all cases percent by weight.

3,343,951 Patented Sept. 26, 1967 ice Aluminum is employed between 5.2% and 6.5% principally to provide elevated temperature strength. Use of less than 5.5% aluminum will not take full advantage of the lightness and strength-imparting characteristics of this element and more than 6.5 will tend to result in thermal instabiltiy. Aluminum as in well known, stabilizes alpha-phase titanium and its presence in such amount as described herein (even with the small amount of beta stabilizer, molybdenum, present), results in a substantially all-alpha type alloy. Such an alloy is preferred for applications requiring welding since heating and cooling as a result of welding or post Welding treatment does not induce deleterious brittleness.

The tin content of the alloy of this invention acts to supplement the aluminum in providing high elevated temperature strength without adverse effect on ductility. Less than 1.7% tin will not provide suflicient of this metal for its effect to be evident, and over 2.3% will be more than required to produce its optimum advantageous effect and also will have adverse effect on the specific gravity of the alloy.

Zirconium functions more as an alpha stabilizer,

, although it does to a degree reduce the beta transes of an alloy in which it is incorporated. Its maximum strengthening effect without serious effect on specific gravity is obtained between 0.7% and 5.0%. Both tin and zirconium form substitutional alpha alloys.

The three elements aluminum, tin and zirconium apparently work in conjunction with each other and with molybdenum, which is beta stabilizer. The amount of molybdenum is also critical since sufiicient must be employed to increase solid solution strengthening and to provide the small amount of beta phase necessary for some heat treatability. Therefore, the amount present should not be less than 0.7% to obtain these results, and more than 3.0% should not be incorporated since the additional retained beta phase will adversely affect weldability and to some extent creep resistance. In addition, molybdenum is a heavy element, twice the specific gravity of titanium, and should be employed only up to an amount at which its benefits more than offset its weight increasing disadvantages.

The oxygen content of the alloy of this invention is also critical and should be present in amount only up to 0.20% and preferably for elevated temperature applications should be present in amount up to 0.16%. Titanium and alloying elements suitable for production of alloys containing less than about 0.08% oxygen are not as readily available and will be often more expensive than those with higher oxygen content.

For the preferred alloys described above, namely 6 A1-2 Sn-2 Zr-l Mo and 6 Al-2 Sn-4 Zr-2 M0, the oxygen content for best stability and elevated temperature properties should be present in amount only up to about a 0.16% and preferably only up to about 0.12%. Oxygen in amount from 0.08% to 0.12% will provide a practical composition within the capability of high grade low oxygen titanium sponge used as a base material.

Oxygen will be found as a constituent in the titanium metal and alloying metals employed to produce the alloy of this invention, and also may be absorbed by the alloy during various phases of preparation as, for example, melting. The oxygen pickup during preparation and melting of the alloy can generally be predicted within reasonable limits and titanium sponge and alloying elements or master alloys can be selected with oxygen content to produce an alloy containing oxygen Within the stated limits. Generally speaking, oxygen below the upper limit as stated is critical to obtain the mechanical properties described, but its presence in some amount, at least a few hundredths of one percent, will be unavoidable using commercial titanium sponge and alloying elements and normally employed melting procedures.

Incidental impurities may be present in the alloy of this invention in amounts associated as impurities in the titanium and alloying metals used. These impurities should not total more than about 0.4% in the aggregate and with respect to the presence of any individual element should not affect the essential nature of the alloy and its properties as herein described. Interstitials, including carbon and nitrogen as well as oxygen should not exceed in the aggregate about 0.25% with the amount of oxygen within the more restricted limits as hereinbefore described.

Density of the alloy of this invention will 'be between 0.16 and 0.17 lb. per cubic inch with the specific figure depending principally on the aluminum and molybdenum content. These elements are the lightest and heaviest respectively in the composition. This range of density includes that of commercially pure titanium, generally accepted to be 0.163 or 0.164 lb. per cubic inch.

The characteristic strength of the alloy of this invention will in general be comparable to or better than the strength of other titanium base alloys such as, for example, those containing Al-2.5% Sn or 6% Al-4% V, balance titanium. The ultimate tensile strength will be at least 120,000 p.s.i. measured at 800 F. Yield strength will be good, in the range of 100,000 p.s.i. and higher; and ductility will be good as indicated by reduction in area and elongation values. Thus the alloy provides high strength yet good ductility.

Another important characteristic is that an alloy according to this invention will show retention of ductility after exposure at elevated temperature under stress. Such retention of ductility is a measure of stability. Elevated temperature properties, particularly stability, will be characteristically good in an alloy of this invention even when the oxygen content is relatively high, that is, over 0.16% and up to 0.20%. However, for best properties and with no degradation of ductility when exposed, for example, for 150 hours at 1000 F. under stress of 30,000 p.s.i. the alloy should preferably contain only up to 0.16% oxygen.

Additionally, the alloy will show creep deformation of less than 0.60% when tested under the same conditions, that is, exposure to 30,000 p.s.i. for 150 hours at 1000 F. Thus the alloy of this invention possesses an unique combination of valuable mechanical properties.

Mechanical properties of the 6% Al-2% Sn-2% Zr-1% Mo type alloy according to this invention are such as to provide an alloy suitable for a variety of purposes. It may, for example, be employed in the manufacture of jet engines Where its strength, ductility and creep resistance are important. For airframe applications, its room and elevated temperature strength will be found advantageous.

For missile applications, its strength and lightness are important. For low temperature use, as in cryogenic bottles and missile liquified gas containers, its low temperature toughness adds to its good other properties.

Following are shown various properties of this alloy:

Density Density of 6% Al-2% Sn-2% Zr-l% Mo, balance titanium alloy is 0.162 lb. per cubic inch. This is comparable to unalloyed titanium and is lighter than many titanium base alloys containing high percentages of heavy metals such as vanadium, iron, molybdenum, columbium or taut-alum.

Room and elevated temperature strength Alloy, 5.7% Al-2% Sn-2% Zr-1% Mo-0.074% O balance titanium; /z-inch sections.

Room temperature strength:

It will be noted that the room and elevated temperature properties are good but not outstanding.

Stability and creep' resistance Sam alloy as above. l /z-inch forged square bar. Heat treated 1800 F. (1 hr.) AC+1100 F. (8 hrs.) AC.

After Exposure to Original 30,000 p.s.i. for 150 Hrs. at 1,000 1'.

Ultimate Tensile Strength, p.s.i 12B, 000 Yield Strength, 0.2+ Ofiset, p.s 114, 000 119, 000 Reduction in Area, Percent- 36 38 Elongation, Percent in 1 inch 18 18 Percent Creep Deformation 0.25

It will be seen that no degradation of tensile ductility occurs after exposure at 1000" F. under stress, and that the deformation due to creep under these conditions is low.

Toughness Same alloy as above. 0.070 sheet annealed at 1450 F. (1 hr.) AC. Specimens machined with NASA sharp notch (Khali Ultimate tensile strength, p.s.i.:

Original 138,000 After 1000 F. for hours+AC 133,000

Toughness [Alloy, 6.0% Al-2.0% Sn-1,8% Zr-1.0% Mo-0.108% Oz-balance titanium] Notch Bend Impact Tensile Properties Room Temp. -80 F.

Dir. Hi 1 I-3 z I-2 3 UTS 4 Y8 6 RA EL 1 %-inch Diameter Bar:

As Rolled L 22.2 20.0 153 143 42 16 1,500 F. (2 Hrs.) AC L 22.8 21.0 141 132 44 19 1,500 F. (2 Hrs.) AC+1,000 F. (4 Hrs.) AC L 21.0 18.5 147 139 43 19 1,750 F. Min.) AG L 31.5 24.8 139 127 46 20 l,750 F. (15 Min.) AC+1,000 F. (4 Hrs.) AC- L 27.0 22.8 144 137 45 21 1,900 F. (5 Min.) AC L 32.0 24.0 136 117 27 16 1,900 F. (5 Min.) AC+1,000 F. (4 Hrs.) AC L 29.2 23.0 139 121 28 15 %-inch Rolled Plate:

As Rnl ri L 20.0 145 136 32 14 Do '1 14. 8 147 141 35 13 1,750 F (15 Min.) AC L 27.8 136 124 33 17 1,750 F (15 Min.) AC T 19.8 136 126 36 15 1,750 F. (15 Min.) AC+1,00 L 36.0 137 128 37 21 l,750 F. (15 Min.) AC+1,00 T 18.0 139 129 85 17 1,900 F. (5 Min.) AC+1,00 T 17. 5 138 125 31 15 1,900 F. (5 Min.) AO+1,00 L 22. 2 136 122 36 20 As Welded 137 123 38 18 1 Foot Pounds, Direction-Longitudinal or Transverse to Rolling Direction.

2 Foot Pounds-The I-3 or Round Impact Specimen is amodificatiou of the I-2. Since it is round it may be turned and notched in a lathe. The dimensions are: 0.452=l:.002 diameter by 2.16.i01 with a 60 notch 1.08 from one end. The root radius of the K notch 0.01=l=.003, and the root diameter under the notch 0.381=|=.002.

3 Foot Pounds-The I-2 or Charpy V Notch Specimen is a conventional one used throughout the industry. It is 0.394d=.001 X0.394;l:.001X2.160=|=.050 with a V notch 1.08 from end; 0.079 deep with a root radius of 0.010i.001. The specimen has exact specifications and must be ground parallel to the long axis to avoid transverse scratches.

4 Ultimate Tensile Strength, K p.s.i.

5 Yield Strength, 0.2% Offset, K p.s.i.

6 Reduction in Area. Percent.

7 Elongation in 1 inch, Percent.

As will be seen from the notch bend impact results in the table above, the alloy of this invention shows good toughness both at room temperature and at 80 F. The tensile strength and ductility in heat treated condition are also good and these properties are not materially degraded in a welded area-note ductility indicated by RA of 38 and Elongation of 18 in the welded specimen.

Mechanical properties of the 6% Al-2% Sn-4% Zr-2% Mo alloy will be similar to those of the 6% Al-2% Sn- 2% Zr-1% Mo alloy except that it will be appreciably stronger although slightly heavier. It will also possess somewhat greater heat treatability. It will find utility in the same general fields as those described for the 6% Al-2% Sn-2% Zr-1% Mo alloy but more specifically where its increased strength will be advantageous and its slightly greater density not too important.

Following are shown various properties of this alloy:

Density Density of 6% Al-2% Sn-4% Zr-2% Mo, balance titanium alloy is 0.166 lb. per cubic inch. This is close to that of unalloyed titanium and is lighter than titanium base alloys containing =high percentages of heavy metals such as vanadium, iron, molybdenum, columbium or tantalum.

Room and elevated temperature strength Alloy, 6.02% Al-2.05 Sn-3.96% Zr-1.86% Mo-.083% O -balance titanium; /2 -inch sections.

Room temperature strength:

Ultimate tensile strength, 'p.s.i 154,000 Yield strength, 0.2% offset, p.s.i. 146,000 Reduction in area, percent 45 Elongation, percent in 1 inch 18 Elevated temperature strength, 800 F.:

Ultimate tensile strength, -p.s.i 123,000 Yield strength, 0.2 oflfset, p.s.i 98,000 Reduction in area, percent- 43 Elongation, percent in 1 inch 20 It will be noted that these room and elevated temperature properties are superior to those for the 6% Al-2% Sll-2% Zr-l% Mo alloy.

Stability and creep resistance Same alloy as above, l /z-inch forged square bar. Heat treated 1775 F. ([2 hr.) AC+1100 F. (8 hrs.) AC.

It will be seen that very little, it any, degradation of ductility occurs after exposure at 1000 F. under stress, and that the deformation due to creep under these conditions is low.

Toughness Alloy, 6.02% A1-2.05% Sn-3.96% Zr-1.86% M0- .083% O 'balance titanium; /2-inch forged square bar.

Notch Notch Heat Treatment Tensile Time Strength 1 Fracture 2 1,775 F. Hr.) AC+1,100 F. (8 Hr.) AC,

p.s.1 232,000 210,000 1,675 F. Hr.) AC+1,100 F. (8 Hr.) AC, p.s.1 234,000 210,000

fNotch tensile strength determined at head speed of 0.05 inch pe r iligih time fracture is the maximum static stress the specimen will withstand for 5 hours without iailure (10 K p.s.i. increments, accuracy better than 1 K psi).

The alloy of this invention may be produced by a convenient method by which the titanium and alloying elements are melted together to form a substantially homo geneous composition. Preferably, titanium sponge of required purity and particularly with respect to its oxygen content is admixed with subdivided aluminum, tin, zirconium, and molybdenum in proper amounts and the mixture compressed into compacts. These compacts are welded together to form an electrode which is melted in a consumable electrode arc melting furnace to produce an ingot of alloy. The so-produced alloy ingot may be itself employed as an electrode in a subsequent remelting step to provide improved homogeneity in a final alloy ingot.

I claim:

1. A titanium base alloy consisting of from 5.5% to 6.5% aluminum, from 1.7% to 2.3% tin, from 0.7% to 5.0% zirconium, from 0.7% to 3.0% molybdenum, and up to 0.2% oxygen, balance titanium except for impurities Within commercial tolerances, characterized by a density between 0.16 and 0.17 lb. per cubic inch, an ultimate tensile strength measured at room temperature of at least 120,000 p.s.i., and stability with creep deformation less than 0.60% after exposure to 30,000 p.s.i. for 150 hours at 1000 F.

2. A titanium base alloy consisting of from 5.5% to 6.5% aluminum, from 1.7% to 2.3% tin, from 0.7% to 5.0% zirconium, from 0.7% to 3.0% molybdenum, from 0.08% to 0.12% oxygen, balance titanium except for impurities within commercial tolerances, characterized by a density between 0.16 and 0.17 lb. per cubic inch, an ultimate tensile strength measured at room temperature of at least 120,000 p.s.i. and measured at 800 F. of at least 70,000 p.s.i., and substantially no degradation of ductility with creep deformation less than 0.60% after exposure to 30,000 p.s.i. for 150 hours at 1000 F.

3. A titanium 'base alloy consisting of about 6% aluminum, about 2% tin, about 2% zirconium, about 1% molybdenum, up to 0.16% oxygen, balance titanium except for impurities Within commercial tolerances, characterized by a density of about 0.162 lb. per cubic inch,

8 an ultimate tensile strength measured at room temperature of at least 120,000 p.s.i. and measured at 800 F. of at least 70,000 p.s.i., and substantially no degradation of ductility with creep deformation less than 0.60% after exposure to 30,000 p.s.i. for 150 hours at 1000 -F.

4. A titanium base alloy consisting of about 6% aluminum, about 2% tin, about 4% zirconium, about 2% molybdenum, up to 0.16% oxygen, balance titanium except for impurities Within commercial tolerances, char- 0 acterized by a density of about 0.166 lb. per cubic inch,

an ultimate tensile strength measured at room temperature of at least 120,000 p.s.i. and measured at 800 F. of at least 70,000 p.s.i., and substantially no degradation of ductility With creep deformation less than 0.60% after exposure to 30,000 p.s.i. for 150 hours at 1000 F.

References Cited UNITED STATES PATENTS 2,868,640 1/1959 Butler 175.5 2,893,864 7/1959 Harris 75175.5 3,049,425 8/1962 Fentiman 75175.5 3,061,427 10/1962 Luhan 75-l75.5 3,105,759 10/1963 Fentiman 75175.5

FOREIGN PATENTS 757,413 9/1956 Great Britain.

HYLAND BIZOT, Primary Examiner.

DAVID L. RECK, Examiner.

C. N. LOVELL, Assistant Examiner. 

1. A TITANIUM BASE ALLOY CONSISTING OF FROM 5.5% TO 6.5% ALUMINUM, FROM 1.7% TO 2.3% TIN, FROM 0.7% TO 5.0% ZIRCONIUM, FROM 0.7% TO 3.0% MOLYBDENUM, AND UP TO 0.2% OXYGEN, BALANCE TITANIUM EXCEPT FOR IMPURITIES WITHIN COMMERICAL TOLERANCES, CHARACTERIZED BY A DENSITY BETWEEN 0.16 AND 0.17 LB. PER CUBIC INCH, AN ULTIMATE TENSILE STRENGTH MEASURED AT ROOM TEMPERATURE OF AT LEAST 120,000 P.S.I., AND STABILITY WITH CREEP DEFORMATION LESS THAN 0.60% AFTER EXPOSURE TO 30,000 P.S.I. FOR 150 HOURS AT 1000*F. 